Vitamin B12 absorption in cystic fibrosis

Vitamin B12 absorption was measured in 30 patients with cystic fibrosis by means of the urinary excretion method and found to be impaired, i.e. less than 10%, in 25. The mean urinary excretion amounted to 4.7 +/- 0.8%. In all patients vitamin B12 absorption improved by the addition of trypsin (18.9 +/- 2.1%). Addition of the vitamin B12 analogue cobinamide, which prevents vitamin B12-binding by R-binders, raised the vitamin B12 absorption to 15.0 +/- 2.2%. A further improvement was obtained by the simultaneous addition of cobinamide and trypsin, 18.2 +/- 2.6%, the same value as with trypsin alone. Assuming that cobinamide addition was effective in suppressing all R-binder activity, the additional effect of trypsin suggests a second, stimulatory function of trypsin on vitamin B12 absorption, separate from R-binder-inactivation. In 5 patients only marginal improvement of vitamin B12 absorption was gained by the addition of either trypsin or cobinamide. The deficient serum vitamin B12 (110 pmol/l) in one of them indicates that the normal pancreas-substitution therapy not always implies sufficient restoration of vitamin B12 absorption.